The Technical Board of Appeal 3.3.06 of the European Patent Office (EPO) has issued a highly significant decision (Case Number: T 2387/22) to revoke European Patent No. 3 325 559, which is held by Sun Chemical Corporation. Dated June 24, 2025, this ruling provides crucial insights into the patentability requirements under the European Patent Convention (EPC), particularly with regard to the clarity (Article 84 EPC) of ‘use claims ‘ when defining technical effects.

The heart of the decision lies in the clarity required when claiming relative improvements of known effects.

The patent was opposed by Schlenk Metallic Pigments GmbH and ECKART GmbH on grounds including lack of inventive step, clarity, and added matter. While various requests were considered, the reasoning of the Board with regard to auxiliary requests 9-11 is of particular interest to intellectual property professionals.

1. Defining technical effects with relative terms: Auxiliary requests 9-11 attempted to define the use of a VMP pigment slurry in a flexographic ink formulation to achieve specific technical effects: ‘fewer print defects, higher hiding and stronger colour and allowing a lower volume anilox’. The patent proprietor argued that the Boards typically allow broad and/or relative terms in non-medical use claims, referencing decisions such as G 2/88.
2. The crucial distinction – New purpose vs. relative improvement: The Board clarified that while use claims can establish patentability by identifying a new technical purpose or effect of a known entity (as in G 2/88 or G 6/88, where a known additive was found to have a new purpose, such as friction reduction rather than rust inhibition), the situation in this case was fundamentally different. In this case, both the claim and the prior art document D10 concerned the same entity (the additive) for the same, or at least an analogous, technical purpose (use in flexographic inks). D10 already reported on printing quality parameters, albeit comparatively inferior ones. Therefore, the claimed technical effects were neither hidden nor unrecognised in the prior art. The alleged technical contribution did not lay in the discovery of a distinct new effect, but rather in the relative improvement or enhancement of already known effects (e.g., better printing quality compared to previously reported results).
3. The requirement for objectively verifiable terms: In such ‘relative improvement’ scenarios, Article 84 EPC ‘generally demands that the feature defining such relative improvement or enhancement be expressed in objectively verifiable terms, thereby ensuring legal certainty regarding the scope of protection‘. The Board found that terms like ‘fewer print defects’, ‘higher hiding’, ‘stronger colour’, and ‘lower volume anilox’ lacked objective assessment criteria. It was impossible to determine objectively when these relative conditions were met, leading to legal uncertainty regarding the claim’s scope. This imprecision blurs the distinction between claimed and known uses.

Other grounds for revocation (in brief):

• Lack of inventive step (Article 56 EPC): For the main request and auxiliary requests 1-8, the Board found no causal link between the distinguishing feature (the selection of specific solvents) and the alleged technical effects (a smoother, glossier finish). The problem was therefore reformulated as merely providing an ‘alternative VMP slurry’, which was considered obvious since prior art D2 had already disclosed preferred solvents within the scope of the claim.
• Added matter (Article 123(2) EPC): Auxiliary requests 12-14 were rejected because their subject matter extended beyond the original disclosure. Specifically, the claim referring to a ‘high-alcohol flexographic ink formulation … containing >50% concentration of an alcoholic solvent’ lacked direct and unambiguous support in the original application, particularly with regard to whether this concentration referred to the slurry or the final ink formulation.

Key takeaway for patent professionals: This decision is a critical reminder for patent practitioners. When drafting ‘use claims’, particularly those defining relative improvements to known technical effects of known entities, it is essential to use objectively verifiable terms to meet the clarity requirements of Article 84 EPC. Vague or imprecise definitions of such improvements can lead to legal uncertainty and, ultimately, patent revocation.